本文紧接
使用重构移除丑陋的if else代码（4）
上篇文章谈到如何能够彻底把这个switch也移除掉呢？很简单，我们只需要在getSystemStatePerformer()方法被调用之前先创建所有
performer匿名类的实例，然后在该方法被调用时直接返回对应的实力。 如何具体实现呢？ 用Map， 请看代码：
package de.jingge.refactoring;
import static de.jingge.refactoring.SystemState.*;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.lang.reflect.Method;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
/**
*
* @author gejing@gmail.com
*/
public class SystemStatePerformerFactory {
private static SystemStatePerformerFactory INSTANCE = new SystemStatePerformerFactory();
private Map<SystemState, SystemStatePerformer> performers;
private SystemStatePerformerFactory() {
}
public static SystemStatePerformerFactory getInstance() {
return INSTANCE;
}
private synchronized Map<SystemState, SystemStatePerformer> getPerformers()
throws Exception {
if (performers == null) {
performers = new HashMap<SystemState, SystemStatePerformer>();
// call all @FactoryMethod using reflection
for (Method m : getClass().getDeclaredMethods()) {
if (m.getAnnotation(FactoryMethod.class) != null) {
SystemStatePerformer p = (SystemStatePerformer) m.invoke(
this, new Object[]{});
performers.put(p.getState(), p);
}
}
// make it readonly
performers = Collections.unmodifiableMap(performers);
&nb